Method for the pyrometallurgical treatment of metals, metal melts and/or slags and injection device

ABSTRACT

In the metallurgical treatment of metals, metal melts and/or slags in a metallurgical unit or melting vessel, especially in electric arc furnaces, injection devices ( 1 ) are used for blowing in or up oxygen-rich gases ( 6 ) and/or carbonaceous substances, which cause as long as possible gas jet ( 6 ′) with a high pulse energy to strike to strike the surface of the slag or metal. It is known to envelope produced gas jet ( 6 ′), thereby focusing it. According to the invention, such an envelope is obtained by using a hot gas ( 5, 5 ′) that is preaccelerated to such a degree that the central gas jet ( 6 ′) is preferably without pulse losses.

The present invention relates to a method of pyrometallurgical treatmentof metals, metal melts and/or slags in a metallurgical installation or amelting vessel, in particular for blowing up or in oxygen-rich gases inan electric arc furnace (EAF) with an injection device which acceleratesoxygen-containing gases to a supersonic speed, with admixing to theoxygen-rich gases, if needed, carbon-containing materials, preferablyparticles, and with an ejected, therefrom, high-velocity jet beingprotected by a gaseous envelope completely enveloping same for using thesame for pyrometallurgical treatment.

Known are injection devices for liquid and particle-shaped material foruse in industrial installations, advantageously, for a pyrometallurgicaltreatment of metal and metal melts, in particular in electrical arcfurnaces for blowing oxygen-rich gases and/or carbon-containingparticles in or up foamed slag layer/slag of an electric arc furnace forfoaming the slag, and/or for blowing up or in of oxygen-rich gases in orup a metal melt, which is located beneath the slag/foamed slag layer forits decarburization. With these injection devices, the oxygen-rich gasis accelerated to a supersonic speed by using a nozzle and, ifnecessary, the carbon-containing particles are admixed to theoxygen-rich gas.

Melting of solid charge materials such as e.g., scrap or spongy iron inelectrical are furnaces requires a large amount of energy (about from550 to 750 kWh/t for ingor steel). In order to reduce the energyconsumption and to shortern the melting time, a chemical energy is added(e.g., natural gas or coal). In order to insure high reactiontemperatures, the combustion is effected primarily with the use of atechnically pure oxygen. Thereby, simultaneously, the amount of theto-be-treated waste gases is noticeably reduced, in comparison with theuse of air. During certain phases of a melting process, for backing upor accelerating scrap heating-up or melting-down, blowing-in of oxygenand/or of the primary energy carrier (e.g., natural gas) takes place.The reaction takes place above the melt, advantageously, in directcontact with the solid material. The addition of the natural gas or ofoxygen is effected with a special burner in the furnace wall or withwater-cooled lances.

A further phase of the pyrometallurgical treatment is the foamed slagphase. The foamed slag should protect or screen the furnace wall fromthe electrical arc radiation during the flat bath phase in order toprevent overheating of the wall regions, to even effectiveness of theelectrical arc, and to provide for a high energy efficiency by reducingthe radiation losses. In order to form the foamed slag, simultaneously,fine-grained carbonaceous materials and oxygen are blown in, preferably,into the boundary layer between the slag and metal.

The addition of the carbon carrier takes place preferably in the regionof the boundary layer between the metal melt and the slag (partiallybeneath the surface of the metal melt). As carriers, advantageously,compressed air, nitrogen, and gaseous hydrocarbons are used.

The injection of the oxygen takes place preferably in the region of theboundary layer between the metal melt and the slag for partial oxidationof powdered carbon and for decarburizaion of the metal melt. During thepartial oxidation of the carbon, which is contained in the carboncarrier, carbon monoxide (CO) is formed. CO is released from slag inform of gas bubbles. They cause foaming of the slag. The foamed slagimproves the energy utilization and reduces the load applied to therefractory brick wall of an electric are furnace. CO can be burnedthereafter inwardly or outwardly by a separate addition of a furtheroxidant.

The addition of carbon carriers, oxygen, and other oxidant is effectedtogether or separately with

-   -   a) special injection-/nozzle devices in the furnace wall    -   b) cooled lances through the door/the furnace wall/the ceiling    -   c) non-cooled lances through the door/the furnace wall/the        ceiling    -   d) nozzle system locatable under the bath.

The devices and methods for the above-described tasks have, inparticular, the following drawbacks.

During the injection of gas/solid material with common injectiondevices, the above-described functions are integrated in a single unit.However, the injected components present, during separate process steps,different and partially contradictory requirements to the associatedinjection system (with regard to flow velocity, the injection site,mixing/burning-out behavior, input into the melt, etc.). Therefore, theunits are very large or compromised solutions should be used.

EPO 0 964 065 A1 discloses an injection device consisting of twocomponents one of which is formed as a supersonic oxygen injector andthe other is formed as a coal injector. The axes of both components areso aligned that the two produced jets intersect each other above thebath surface. In order to insure focusing of the central oxygen or thecoal jet to a most possible extent, they are enveloped with a naturalgas jet that is ejected through a nozzle ring surrounding the centralnozzle opening.

U.S. Pat. No. 5,904,895 discloses a water-cooled injection device with acombustion chamber for producing a high-speed flame for melting downsolid materials located in front of the combustion chamber. As meltingprogresses, fine-dispersed solid materials, e.g., coal, and anadditional oxygen can be brought into the electric arc furnace, with thesolid material being admixed sidewise to the already accelerated oxygenjet. Both, the jet of the solid material and the high-speed oxygen jetare protected by a surrounding them, flame envelope.

EPO 0 866 138 discloses a method of injecting gases (e.g., oxygen and anatural gas) into the melt. Here, oxygen which is ejected centrally froman injector, is accelerated to a supersonic speed with a Laval nozzle.In order for the jet to retain its outer pulse straight as long aspossible, it is protected by a flame envelope that surrounds it(completely). The flame envelope is produced by combustion of a naturalgas which is ejected through an annular slot or a nozzle ring, whichconcentrically surrounds the Laval nozzle, and oxygen. The oxygen is fedthrough a second annular slot or nozzle ring which is concentricallyarranged outwardly of the natural gas ring.

EP1 092 788 A1 discloses an injection device which is based on theprinciple of EP 0866 138 A1 and additionally includes injection of aparticle-shaped solid material. The injection of the solid material iseffected in the same way as injection of oxygen, inside of a flameenvelope.

EP 0 848 795 discloses a method of coombustion of fuel and an associatedburner. As fuel, both natural gas and a particle-shaped solid materialare used. Here, several natural gas jets, which are inclined toward thecentral axis, are blown in a cylindrical or slightly cone-shaped mainoxygen jet that widens in the jet direction. A Laval nozzle acceleratethe jet to a supersonic speed. The fuel jets surround the main jet andpenetrate thereinto downstream. Within the main stream, a second fueljet is formed by using a central tube, with the natural gas or the solidmaterial being sprayed into the main jet after its acceleration.

In order to delay widening of the jets over their paths as long aspossible, when injection devices are used, the produced jets aresurrounded several times with a flame envelope that is usually producedby combusting a natural gas. The drawback of a flame envelope consistsin an undesirable pulse loss of the central jet because the flowvelocity of the envelope jet is substantially lower than that of thecentral jet. In addition, this measure requires use of additionalmaterials and, therefore, is associated with high energy costs. This iswasteful from the technological point of view and is also at timesineffective.

Proceeding from the known state of the art, the object of the inventionis to provide an injection device and a method with which it would bepossible to maximize the length of a jet of an oxygen-rich gas thatflows free in the inner space of a metallurgical installation, and itspenetration depth into the slag layer. Here, in particular, thedrawbacks of the known devices for common injection of oxygen and solidmaterial at different operational conditions namely

-   -   high energy consumption    -   necessary manipulations or provision of several openings in the        metallurgical installation    -   complicated construction        should be eliminated to a most possible extent.

The object of the invention is achieved with a method, which is based onthe use of an injection device, with features of the characterizedclause of claim 1, namely, that a hot gas forms a gaseous envelope andis so fed to the central high-speed jet that the relative speed and thepulse exchange between the high-speed central jet and the hot gasenvelope jet is minimized (quasi isokinetic feeding).

An injection device for effecting the inventive method is characterizedby features of claim 17. Advantageous embodiments and developments ofthe invention follow from related dependent claims.

With the inventive method, enveloping of the central oxygen-rich gas jetwith hot gas with as small as possible pulse loss, permits,advantageously, to maximize the length and the penetration depth of thegas jet into the slag layer located above the metal melt for obtainingof an intensive intermixing and movement, and to improve injection of aparticle-shaped solid material, e.g., carbon carrier, dust, oradditives.

At that, the central gas jet is. injected with an oxygen injector (along tube with a Laval nozzle) and is accelerated to a speed between 300and 850 m/sec and, contrary to the known solutions, is enveloped with ahot gas envelope. The hot gas is produced by an external combustion in ahot gas generator, e.g., by combustion of a natural gas-air mixture in aconventional high-speed burner, by recirculation of hotter furnace gasesusing a separate high-temperature compressor, or by combination of bothmethods.

When the hot gas is produced by an external reaction of fuel with anoxidant, an oxidant with an oxygen content from 10 to 100% by volumeand, preferably, 21% by volume is used. The oxidation process in eachcase is effected leaner than stoichometrically. The air ratio in the hotgas generator is set between 1.05 and 2.0 (preferably 1.3-1.5). Theoxidant can be preheated to a temperature between 50° C. and 600° C.(preferably between 200° C. and 400° C.). The preheating can take placeexternally or in the injection device. Preferably, The preheating of theoxidant is integrated into the cooling system of the injection device orforms its essential component.

The temperature of the hot gas upon entry in the torch amounts from 300°C. to 1,800° C. In this temperature region, the sonic speed of the hotgas, as a result of thermodynamic relationships on which the process isbased, is substantially higher than that of a cold central jet.Therefore, the exit speed of the hot gas is lifted up to the region ofspeeds of the central jet with a simple nozzle.

According to the invention, for a temperature control, it is possible toinject water into the hot gas before its acceleration. Thereby, a rapidand precise temperature control is insured. In addition, an increasedcontent of water vapors positively influences the reaction atmosphere inthe furnace well.

The injection device of the invention consists, in modularimplementation, of a long tube with a Laval nozzle, an oxygen injectorfor acceleration of the oxygen-rich gases the outlet region of which issurrounded by an annular slot nozzle or a similar construction with acomparable action for passing of the hot gas therethrough. For focusingand for improving flow ratios in the outlet plane, the outlet regions ofboth gases are extended by a hot gas sleeve.

For injection of particle-shaped materials, there is arranged centrallyin the oxygen injector an additive injector in form of an additionalcoaxial tube with an outlet opening. The additive injector is axiallydisplaceable. The outlet plane of the additive injector can bepositioned (viewed in the flow direction) both in front of and behindthe inlet cross-section of the confusor of the Laval-nozzle of theoxygen injector. The positioning of the outlet opening of the additiveinjector within the oxygen injector can be effected by an axialdisplacement of the additive injector, of the oxygen injector or by thecombination of both. The outlet opening of the additive injector can beformed as a simple mouth or as a nozzle. Preferably, the outlet openingof the additive injector is position in front of the Laval nozzle of theoxygen injector, so that the particle-shaped material is accelerated,together with the oxygen-rich gas, by the Laval nozzle.

Because of a high wear which is caused by load applied by theparticle-shaped material, the outlet opening of the additive injector isformed of a wear-resistant material. For protection of the outer shellof the oxygen injector, it can be provided with a ceramic protectionlayer or be surrounded with a ceramic protection tube.

It is also possible to inject, through the additive injector into theoxygen-rich gas jet, other material than a particle-shaped material,e.g., a gaseous fuel, such as natural gas, or a liquid fuel such as oil.In order to adapt to different special demands of respective fuels,different embodiments of additive injectors are necessary. Those arerapidly adaptable, and with only low costs, by provision of suitableconstructions, to respective process requirements and are provided,e.g., with a replaceable outer nozzle and suitable additional elements,and are made axially displaceable, manually or automatically.

The injection device for injecting gas or solid materials is formed as amodular construction. Separate components are mounted on a commonsupport fixedly secured in a wall of a metallurgical installation.Thereby, an undesired entry of the surrounding air into the furnace welland a dangerous exit of the reaction gases in the environment isreliably prevented.

The injection device can be universally used for adding during separatephases of a metallurgical process, necessary materials (oxygen, oxygencarriers, additives, etc.) in the necessary quantity and with thenecessary quality as a result of formation of robust and constructivelysimple components. This guarantees small maintenance and installationcosts and provides, if needed, for rapid replacement of separatecomponents even during operation of a furnace.

To insure a high efficiency of the injection system, more than oneinjection device can be provided for a meting installation (preferablyfrom two to four). The operation of the injection device is coordinatedand monitored by an overriding system.

Further advantages, particularities, and features of the invention willbe explained in detail below with reference to schematic drawings whichshow in embodiments of the invention.

The drawings show:

FIG. 1 a cross-sectional view of an injection device according to theinvention (basic version);

FIG. 2 a cross-sectional view of the injection device shown in FIG. 1with an injector of additives;

FIG. 3 a flow diagram of the injection device; and

FIG. 4 measurement and control diagram (flow chart) of the injectiondevice.

FIG. 1 shows a schematic cross-sectional view of an injection device 1according to the invention which in the shown embodiment essentiallyconsists of an angled hot gas union 2 into which an oxygen injector 10is inserted sidewise. The insertion of the oxygen injector 10 iseffected, preferably, in such a way that the longitudinal axis of theoxygen injector 10 coincides with the longitudinal axis of thehorizontal portion of the injection device 1. At its front, at the rightof the drawing, the inner diameter of the hot gas union 2 is reduced byan inclined inward thickening 7 (confusor) to such an extent that thehot gas union 2 forms with the oxygen injector 10 in this region aconcentric annular slot nozzle 4 or constructively similar means with acomparable action (referred to below as annular slot nozzle forsimplicity sake).

The oxygen injector 10, which is inserted in the hot gas union 2,consists of an elongate tube or an injector inner wall 11 surrounded bya ceramic protection layer 12 and having a Laval nozzle 13 in its frontregion. The oxygen-rich gas 6 flows through the Laval nozzle 13 in thedirection shown with arrow, is accelerated, and is ejected from outletopening 14 in the direction shown with arrow as a central gas jet 6′. Inthe outer region the oxygen-rich gas jet 6′ is enveloped by the flowingin the same direction, hot gas 5′ which is accelerated in the annularslot nozzle 4. For focussing the gas jets 5′, 6′, the outer region iselongated by a hot gas sleeve 3 the inner diameter of which correspondsto the smallest outer diameter of the annular slot nozzle 4.

The oxygen injector 10 is axially displaceable, with its outlet plane 5being positioned between planes 3 and 4 of the hot gas union 2 in anyarbitrary position of the oxygen injector.

FIG. 2 shows an injection device 1 that in comparison with the injectiondevice 1 of FIG. 1, further includes an additional additive injector 15and water spray means 18. The same components are shown with the samereference numeral for a better understanding. The water spray means18 islocated in the entry region of the injection device 1 in the hot gasunion 2 and is so arranged that the water 19 is injected in this regionin a direction opposite the flow direction of the hot gas 5 in thisregion. The oxygen injector 10 is not any more surrounded by a ceramicprotection layer, as in the embodiment of FIG. 1, but is held with aceramic protection tube 17. The additive injector 15 consistsessentially of an elongate tube with a front fuel nozzle 16 and isinserted in the oxygen injector 10 so far that the opening of the nozzle16 is located in front of the Laval nozzle 13 of the oxygen injector 10.In this way, carbon-containing materials 8, 8′ and the oxygen-reach gas6′ are ejected together from the outlet opening 14 as a central jet 9.

FIG. 3 shows a principle scheme of feeding of media necessary for theoperation of the injection device 10 and a typical circuitry of theinjection device 1. The hot gas 5 is produced in an external separategenerator 20 from a fuel stream 8 and a stream of the oxygen-rich gas 6.Advantageously, the hot gas generator 20 is directly connected with theinjection device 1 or forms an essential component thereof. In the shownembodiment, an oxidation air 23 is used. The air 23 can be fed by aseparate blower 21 or from a compressed air network 22. The air 23 isused, before it is fed to the hot gas generator 23, for cooling theouter wall of the injection device 1. It is preheated to temperaturesfrom 50° to 600°. The preheating positively influences the treatment offuel in the hot gas generator 20. The operation of the hot gas generator20 is not interrupted. The same is true for the cooling system. Byactuation of stop valves 25, 26, 27, the feeding of a respective mediumstream is started or interrupted. The regulation of the flow volume iseffected with control valves 28, 29, 30. During injection of oxygen, themulti-way valve 31 is closed in such a way that air flow to the oxygeninjector is interrupted. When for technological reasons, no oxygeninjection is necessary, the multi-way valve 31 is closed in such a waythat the oxygen flow to the oxygen injector is interrupted. In thiscase, air 23 is fed to the oxygen injector 10.

FIG. 4 shows a measurement and control diagram (flow chart) for theinjection device 1. For a reliable operation of the injection device 1accordance with regulations, the positions of the stop valves 25, 26, 27should be monitored and changed in a controlled manner. The occurrencesof non-permitted and/or dangerous operational conditions is prevented bycorresponding locking/blocking. A central automation unit R communicateswith an overriding PCS (process control system) of a metallurgicalinstallation and communicates, in accordance with the operating mode,necessary commands to subordinate units as well as R1 and R2. Theautomation unit R1 is responsible for controlling the hot gastemperature, output of the hot gas generator, and the air ratio. Thenecessary process parameters are continuously acquired withcorresponding sensors and are transmitted to a computer. The automationunit R2 serves for controlling of the oxygen volume.

The control of the operation of the additive injector 15 is effected bya further automation unit (e.g., for mass flow, admission pressure).This control is represented in FIG. 4 by automation unit R3.

According to the invention, several preferably, from two to fourinjection devices can be associated with a metallurgical installation.For common control of these injection devices 1, a data exchange takesplace between the automation unit R and the PCS.

List of Reference Numerals

-   1 Injection device-   2 Hot gas union-   3 Hot gas sleeve-   4 Annular slot nozzle-   5,5′ Hot gas-   6,6′ Oxygen-rich gas-   7 Thickening-   8 Fuel-   9 Central jet-   10 Oxygen injector-   11 Injector inner wall-   12 Ceramic protection layer-   13 Laval nozzle-   14 Outer opening-   15 Additive injector-   16 Outer opening-   17 Ceramic protection tube-   18 Water spray means-   19 Water-   20 Hot gas generator-   21 Blower-   22 Compressed air network-   23 Air-   25,26,27 Stop valves-   28, 29, 30 Control valves-   31 Multi-way valve-   1 Further injection devices-   PCS Process control system-   R Central automation unit-   R1 Automation unit-   R2 Automation unit-   R3 Automation unit

1-24. (Canceled).
 25. Method of pyrometallurgical treatment of metals,metal melts, and/or slags in a metallurgical installation or a meltingvessel, in particular for blowing up or in oxygen-rich gases inelectrical are furnace with an injection device with acceleratesoxygen-containing gases (6) to a supersonic speed, with an ejected,therefrom, high-velocity jet (6′) being protected by a gaseous envelopecompletely enveloping same for using the same for pyrometallurgicaltreatment, characterized in that the gaseous envelope is formed of a hotgas (5) that is so fed to the central high-velocity jet (6′) thatrelative speed and pulse exchange between the central high-velocity jet(6′) and the hot gas enveloping jet (5′) is minimized (quasi isokineticfeeding), the oxygen-rich gas (6) is accelerated in an injection device(1) in a nozzle system (preferably in Laval form) to a speed from 300 to800 m/sec, and the hot gas (5) is accelerated to approximately samespeed with an annular slot nozzle (4) of the injection device (1), withthe hot gas (5) having a temperature from 300 to 1,800° C. upon enteringthe injection device.
 26. A method according claim 25, characterized inthat the hot gas (5) becomes available due to an external reaction offuel (8, 8′) with an oxidant and/or as a result of recirculation of hotgases from the metallurgical installation.
 27. A method according toclaim 26, characterized in that for producing of the hot gas, apreheated oxidant with an oxygen content from 10 to 100% by volume,preferably, 21% by volume is used.
 28. A method according to claim 25,characterized in that the preheating of the oxidant is integrated in acooling system of the injection device (1) and/or forms an essentialcomponent thereof.
 29. A method according to claim 27, characterized inthat adjustment of hot gas temperature in front of the injection device(1) is effected by controlling power of a hot gas generator (20) and/orby adding water (19) to the hot gas before its acceleration.
 30. Amethod according to claim 25, characterized in that an oxygen content ofthe oxygen-rich gas (6) amounts from 10 to 100% by volume, preferably,more than 95% by volume.
 31. A method according to claim 25,characterized in that particle-shaped solid materials and/or liquidmaterial (8), if needed, is fed to the central oxygen jet (6), whereinfeeding of these substances is effected with an additive injector (15)coaxially arranged in the oxygen injector (10) in the same direction andbefore an end of the acceleration process.
 32. A method according toclaim 31, characterized in that the particle-shaped solid materialcontains carbon (e.g., coal or coke dust), alkali and/or alkali earthmetals (e.g., limestone, unhydrate lime, or dolomite, and the fluidmaterial (8′) contain carbon (e.g., natural gas, coke gas, convertergas, heating oil), respectively, in high concentration (more than 30% byweight).
 33. A method according to claim 25, characterized in that theoxygen injector (10) operates alternatively with a technical oxygen andair, wherein a switch from oxygen supply to air supply and back iseffected by using (31), and for air supply, an oxidant source or anothersource, e.g., a compressed air network (22) or a blower (21) is used.34. A method according to claim 25, characterized in that the control ofthe operation of the hot gas generator (20), e.g., λ-control ofcombustion, the control of the hot gas temperature, the control of acooling exit temperature, etc. is effected by an automation unit (R1).35. A method according to claim 25, characterized in that the control ofthe operation of the oxygen injector (10), e.g., volume flow, admittancepressure, etc. is effected by an automation unit (R2).
 36. A methodaccording to claim 25, characterized in that the control of theoperation of the additive injector (20), e.g., mass flow admittancepressure, etc., is effected by a further automation unit (R3).
 37. Amethod according to claim 25, characterized in that more than oneinjector devices (1), preferably from two to four, are provided on themetallurgical installation.
 38. A method according to claim 25,characterized in that coordination of operation of the automationdevices (R1, R2, R3) is effected with an overriding central automationunit (R) that stands in data exchange with a process control system(PCS) of the metallurgical installation, or is self-sufficient, whereinthe data exchange is effected with corresponding automation units of theinjection devices (1).
 39. An injection device (1) for pyrometallurgicaltreatment of metals, metal melts, and or slags in a metallurgicalinstallation or a melting vessel, in particular for blowing up or inoxygen-rich gases and/or carbon-containing material in an electric arcfurnace, wherein the injection device accelerates oxygen-containinggases, (6) to a supersonic speed, with an ejected therefrom,high-velocity jet (6′) being protected by a gaseous envelope completelyenveloping same for using the same for pyrometallurgical treatment,characterized by a modular construction of separate subassembliesconsisting of an oxygen injector (10) with an inner wall (11) and aLaval nozzle (13) for accelerating an oxygen-rich gas (6), which issurrounded by a hot gas union (2) in an outlet region of which isarranged an annular slot nozzle (4) or similar constructed means with acomparable action for passing and acceleration of a hot gas (5).
 40. Amethod according to claim 39, characterized in that the oxygen injector(10) is axially displaceable and wherein an outlet plane (5) of theoxygen injector (10) in each position thereof is located between planes(E3) and (E4) of the hot gas union (2).
 41. An injection device (1)according to claim 39, characterized in that outlet regions of the gasesare extended by a common hot gas sleeve (3).
 42. An injection device (1)according to claim 39, characterized in that in the entrance region ofthe hot gas union (2), water spray means is arranged.
 43. An injectiondevice (1) according to claim 39, characterized in that within thecentral oxygen injector (10), an additive injector in form of anadditional coaxial tube with an outlet opening (16), which is formed asa mouth or nozzle, is arranged.
 44. An injection device (1) according toclaim 43, characterized in that the outlet opening (16) of the additiveinjector (15) is formed of a wear-resistant material and is replaceable.45. An injection device (1) according to claim 43, characterized in thatthe additive injector (15) is axially displaceable and is positionedwith its outlet plane (B) between planes (E1) and (E2) of an oxygeninjector (10).
 46. An injection device (1) according to claim 39,characterized in that separate subassemblies of the injector device (1)are mounted on a common support arranged in a wall of the metallurgicalinstallation.